6.1 Extracting vegetable oil
Some seeds , nuts and fruits are Rich in Vegetable oils. The oils can be extracted by crushing and pressing the plant material, followed by removing water and other impurities.
When eaten Vegetable Oil can provide us with a lot of energy and important nutrients. They also release a lot of energy when burned so they can be used as fuels.
· Molecules in vegetable oil have hydrocarbon chains. Those carbon-carbon double bonds(C=C) are unsaturated. Several double bonds in each molecule, this is called Polyunsaturated. Unsaturated oils react with bromine water, turning from orange to colourless.
6.2 Cooking with Vegeatable oils
Boiling point of vegetable oil is higher than water, so food is cooked at higher temperatures in oil. This means it cooks faster, and it changes the flavour, colour, texture of the food.
Some oil is absorbed and so the energy content of the food increases.
Unsaturated oils can be reacted with hydrogen so that some or all carbon double bonds become single bonds. This reaction is called hydrogenation and is done at about 600 degree Celsius using a nickel catalyst.
Hydrogenated oils have higher melting points because they are more saturated. Reaction called hardening because the hydrogenated oils are solids at room temperature.
· This means they can be used as spreads and to make pastries and cakes that require solid fats.
6.3 Everyday Emulsions
Oil and water do not mix and separate from each other, forming two layers. If we shake, stir, beat the liquids together tiny droplets form that can be slow to separate. This is called EMULSION.
· Emulsions are opaque and thicker than oil and water they are made from, improves the texture, appearance and their ability to coat and stick solids.
o Milk, cream, salad dressings, ice cream, water based paints and many cosmetic creams are examples of emulsions.
Emulsifiers are substances that help stop the water and oil separating into layers. Most emulsions have emulsifiers to keep them stable.
6.3 Everyday Emulsions
Emulsifier molecules have small hydrophillic part and a long hydrophobic part. Hydrophillic part'head' is attracted to the water. Hydrophobic part ' tail' is attracted to the oil. Hydrophobic parts of many emulsifiers molecules go into each oil droplet, and so the droplets become surrounded by the hydrophillic parts. This keeps the droplets apart from the water, preventing them from joining together and seperating out.
6.4 Food Issues
Benefits of Vegetable oils and Emulsifiers.
· Vegetable oils contain important nutrients and are high in energy. Contain unsaturated fats, believed to be better than saturated fats for our bodies.
· Emulsifiers stop oil and water separating into layers making our food smoother, creamier and more palatable.
Drawbacks of Vegetable oils and Emulsifiers.
· Animal fats and hydrogenated vegetable oils contain saturated fats and are used in many foods. Saturated fats have been linked to heart disease.